The present invention relates to novel ophthalmic lens materials and a method for making and using the same. More particularly, the present invention relates to soft, optically transparent, high refractive index hydrogel materials particularly suited for use in the production of intraocular lenses, and a method for manufacturing and using the same.
Since the 1940""s optical devices in the form of intraocular lenses (IOLs) have been utilized as replacements for diseased or damaged natural ocular lenses. In most cases, an intraocular lens is implanted within an eye at the time of surgically removing the diseased or damaged natural lens, such as for example, in the case of cataracts. For decades, the preferred material for fabricating such intraocular lenses was poly(methyl methacrylate), which is a rigid, glassy polymer.
Softer, more flexible IOLs have gained in popularity in recent years due to their ability to be compressed, folded, rolled or otherwise deformed. Such softer IOLs may be deformed prior to insertion thereof through an incision in the cornea of an eye. Following insertion of the IOL in an eye, the IOL returns to its original pre-deformed shape due to the memory characteristics of the soft material. Softer, more flexible IOLs as just described may be implanted into an eye through an incision that is much smaller, i.e., less than 4.0 mm, than that necessary for more rigid IOLs, i.e., 5.5 to 8.0 mm. A larger incision is necessary for more rigid IOLs because the lens must be inserted through an incision in the cornea slightly larger than the diameter of the inflexible IOL optic portion. Accordingly, more rigid IOLs have become less popular in the market since larger incisions have been found to be associated with an increased incidence of postoperative complications, such as induced astigmatism.
With recent advances in small-incision cataract surgery, increased emphasis has been placed on developing soft, foldable materials suitable for use in artificial IOLs. In general, these materials fall into one of three categories: hydrogels, silicones and low glass transition temperature acrylics.
In general, high water content hydrogel materials have relatively low refractive indexes, making them less desirable than other materials with respect to minimal incision size. Low refractive index materials require a thicker IOL optic portion to achieve a given refractive power. Silicone materials may have a higher refractive index than high-water content hydrogels, but tend to unfold explosively after being placed in the eye in a folded position. Explosive unfolding can potentially damage the corneal endothelium and/or rupture the natural lens capsule and associated zonules. Low glass transition temperature acrylic materials are desirable because they typically have a high refractive index and unfold more slowly and more controllably than silicone materials. Unfortunately, low glass transition temperature acrylic materials, which contain little or no water initially, may absorb pockets of water in vivo causing light reflections or xe2x80x9cglisteningsxe2x80x9d. Furthermore, it is difficult to achieve ideal folding and unfolding characteristics due to the temperature sensitivity of the acrylic polymers.
U.S. Pat. No. 5,480,950 issued Jan. 2, 1996 teaches of high refractive index hydrogel materials having a hydrated equilibrium water content of at least 57% for use in the manufacture of IOLs. The high refractive index hydrogel materials are cross-linked polymers prepared from mixtures of N-vinylpyrrolidone, 4-vinylpyrimidine and a vinyl pyridine having equilibrium water contents up to 90% and refractive indexes of 1.560 to 1.594 in the dry state. The IOLs as described are not implanted in a hydrated state. Rather, the IOLs are implanted in a dry, folded and elongated state and hydrated in situ. The refractive indexes in the hydrated state as used in the eye are not provided.
U.S. Pat. No. 5,693,095 issued Dec. 2, 1997 teaches of high refractive index, low water content IOL materials. The materials taught in this particular patent are acrylic materials having an elongation of at least 150%. IOLs manufactured from a material having such elongation characteristics will not crack, tear or split when folded. However, such low water content acrylic materials have been found to be less biocompatible than higher water content hydrogel materials when manufactured into and used as IOL devices.
Soft, foldable hydrogel lens materials having relatively high water contents and unexpectedly high refractive indexes particularly suited for use as intraocular lenses (IOLs), or other ophthalmic devices such as but not limited to contact lenses, keratoprostheses and corneal rings or inlays, have now been discovered. The subject hydrogel lens materials contain only two principal components: a high refractive index monomer that is usually hydrophobic but not necessarily so, and a hydrophilic monomer. The hydrogel materials of the present invention are copolymers comprising at least about 70% by weight of the two principal monomeric components whereby the hydrophilic monomer is present in an amount greater than that of the high refractive index monomer to maximize water content. The remainder of the hydrogel material formulation comprises up to approximately 30% water, cross-linkers, initiators, UV absorbers and like additives.
Accordingly, it is an object of the present invention to provide a biocompatible IOL material having a high refractive index
Another object of the present invention is to provide a hydrogel IOL material having a high refractive index
Another object of the present invention is to provide a hydrogel IOL material that has a high refractive index and is colorless.
Another object of the present invention is to provide a hydrogel IOL material that has a high refractive index and is transparent.
Still another object of the present invention is to provide a hydrogel IOL material that is relatively simple to manufacture.
These and other objectives and advantages of the present invention, some of which are specifically described and others that are not, will become apparent from the detailed description and claims that follow.